i know a hb9, i already have her number. today i talked to her for the second time and in the end i didn't know how to make her want to call/ text me again. i just said see you later, that's it. before, she playfully said "maybe" in response to my question if she's going to call me. how should i have ended the encounter?

All I can say is you probably shouldn't have asked her if she was going to call you again. That was definitely a "desperate" move, never good.

One easy way to get a call back is by finding out if she is going to a event in the near future (a day or two, no longer) and asking her if you can go along. Tell her to txt or call you, then when she does you can spark some convo or at least have another meeting place.

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"I have only one counsel for you - be master."

She's not going to call u again, unless you give her a reason to. She's an HB9. U think your the only guy calling her. Start off my asking how she's doing, and bring up something she mentioned about herself, eg. her job.. Then babble on about it.. Then.. transition.. this is where you have to be specific.. That "let's hang out" is bad. You have to be specific. Date/location/Activity.. Girls plan what they're diong days ahead. They know when and with who they're going shopping. THey know which clubs they're going to every time they go out... You have to speak their language. Pitch a nice spot, and make it seem only cuz your doing her a favor. Wow.. all u do is work.. how about tomorrow at 6, U come with me, to So&so restaurant/bar, at around 7. I'll txt u around fivish-six. be specific..

Such a wise idea to ask if you can tag along, as oppose to the opposite?
How would you even get her interested by starting off with boring talk?

well.. thats a good question. Some girls give out phone numbers regardless whether they're interested or not. They do this because they don't like being mean. If you gamed her correctly BEFORE you get her phone number, then you'd have plenty of things to talk about, so it wouldn't necessarily be boring talk. Gaming is all about getting the girl comfortable with you. The phone call should sound like you calling an old freind. I don't know anything about your interaction with the girl before you got her number so I cant be more specific.